1. Field of the invention
This invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus which have the photosensitive member.
2. Related Background Art
Electrophotographic photosensitive members are constituted basically of a photosensitive layer on which a latent image is formed by electrostatic charging and exposure to light and a substrate on which the photosensitive layer is provided.
Meanwhile, electrophotographic photosensitive members are required to have sensitivities, electric properties and optical characteristics in accordance with electrophotographic processes applied.
They are also required to have an environmental stability in any environment of from low temperature/low humidity to high temperature/high humidity so as to sufficiently exhibit their performances.
Faulty images are exemplified typically by white lines, black spots in white background areas, white spots in black background areas, background fog in white background areas, and also interference fringes caused by factors such as surface shape of substrates and uneven layer thickness of photosensitive members in the case of apparatus such as digital copying machines and laser beam printers in which exposure is effected using a light source having a single wavelength. Accordingly, in the manufacture of photosensitive members, some countermeasures must be taken so that these faulty images do not occur.
As a factor having a great influence when such faulty images occur, the surface state of a substrate may be key.
Substrates having not been treated at all after molding, in general, do not necessarily have an optimum surface state for photosensitive members. Hence, problems caused by the surface state may occur in many instances.
To solve such problems, some approaches have hitherto been proposed, as exemplified by a method in which the surface of an aluminum substrate is subjected to chromate to form a chromate chemical conversion coating, as disclosed in Japanese Patent Application Laid-open No. 54-12733 and No. 57-62056; a method in which a boehmite coating is formed on the surface of an aluminum substrate, as disclosed in Japanese Patent Application Laid-open No. 58-14841 and No. 64-29852; and a method in which the surface of an aluminum substrate is oxidized forcedly by high-temperature treatment to form an oxide film, as disclosed in Japanese Patent Application Laid-open No. 57-29051.
With regard to, e.g., the method of chromate treatment, substrates having a good performance to a certain degree can be obtained. However, since treating solutions contain chromium, it is very difficult to dispose of waste liquor, and also this is not preferable in view of environmental safety.
With regard to the boehmite treatment, the crystal state of the surface can not be said to be suited for substrates of electrophotographic photosensitive members. It can be effective to a certain degree with regard to electrophotographic performance, but, with regard to images, no satisfactory image quality has been achieved because the surface structure and shape are unsatisfactory. Thus, under existing circumstances, those satisfying all performances have not been available.
The aim of the above surface treatment is to form on the substrate surface a coating which prevents any non-uniformity in electrophotographic performances and images from occurring due to electric charges injected locally from the substrate into the photosensitive layer.
As a method of preventing such local charge injection so as to prevent faulty images, a method is available in which the surface of an aluminum substrate is subjected to anodizing to provide a layer of aluminum oxide (e.g., Japanese Patent Application Laid-open No. 2-7070 and No. 5-34964).
This method is a good method in order to attain such an aim. However, in order to form the layer uniformly without causing any uneven layer thickness on the substrate surface, it must be formed thicker about 5 or 6 .mu.m or more under the usual conditions for its formation. Hence, the layer must be formed in a much larger thickness than the thickness actually required as a charge injection blocking layer, resulting in an increase in cost.
Semiconductor lasers prevailingly used at present in laser beam printers and so forth have a relatively long oscillation wavelength as long as 790.+-.20 nm. Accordingly, as charge-generating materials used in photosensitive layers, those having sufficient sensitivities to such a long-wavelength light are being studied.
In particular, much research has been conducted on phthalocyanine pigments because of their good sensitivities to long-wavelength light.
The phthalocyanine pigments may include, e.g., metal-free phthalocyanine, copper phthalocyanine, aluminum chlorophthalocyanine, oxyvanadyl phthalocyanine, oxytitanium phthalocyanine, chlorogallium phthalocyanine and hydroxygallium phthalocyanine. Most of these phthalocyanine compounds are known to have various crystal forms.
With regard to the chlorogallium phthalocyanine and hydroxygallium phthalocyanine having especially high sensitivities to long-wavelength light, they also have many crystal forms. As to the chlorogallium phthalocyanines, they are disclosed in Japanese Patent Application Laid-open No. 1-221459, No. 5-98181, No. 5-194523, No. 5-247361, No. 6-73303, No. 7-53891 and No. 7-207171. As to the hydroxygallium phthalocyanines, they are disclosed in Japanese Patent Application Laid-open No. 5-236007, No. 5-279591, No. 6-93203, No. 6-279698 and No. 7-53892.
With regard to the oxytitanium phthalocyanine, it also has many crystal forms. For example, oxytitanium phthalocyanines having different crystal forms are reported in Japanese Patent Application Laid-open No. 61-239248, No. 62-67094, No. 1-17066, No. 3-128973 and No. 3-54265.
However, compared with azo pigments, these phthalocyanine compounds tend to affect charge stability or image stability as a result of extended operation or depending on environment, and also tend to cause a problem of a rise in residual potential, ascribable to substrates or subbing layers. Accordingly, studies are made on electrophotographic photosensitive members that can satisfy these performances at a higher level.